Community ecology and spatio-temporal patterning of abyssal invertebrates in the Clarion Clipperton Zone

Abstract

The abyssal zone (> 3500 m) represents an important biodiversity reservoir due to its vast size, species richness, and high rates of community turnover. Most abyssal invertebrate communities are poorly described, including the environmental drivers of diversity and biogeography. These communities are susceptible to species extinction and reduced ecosystem services with forthcoming anthropogenic impacts, including climate change and deep-sea mining. The Clarion-Clipperton Zone (CCZ), a 6 million km2 region of the Eastern Pacific, is characterized by abundant and mineral-rich polymetallic nodules that are of increasing economic and technological interest to support renewable energy development. Baseline descriptions of ecology and biogeography in the CCZ can be used to test hypotheses about the maintenance of diversity in the deep sea, in addition to meaningful applications toward management objectives. This dissertation addresses the community ecology and spatiotemporal patterning of abyssal marine invertebrates of the CCZ. Chapter 1 provides the environmental and management background of the CCZ as well as a brief literature review of faunal communities occupying sediments, nodules, and benthic boundary layer (BBL) seawater and their associated ecological patterns. In Chapter 2, patterns of diversity at the scale of a mining license area (10-100 km) were evaluated across habitats using a multigene, environmental DNA approach from seafloor sediments (24 cores; 0 – 2 cm, 2 – 5 cm in triplicate), and the targeted mineral deposits, polymetallic nodules (365 nodules) from the NORI-D license area. Nodule-obligate taxa contributed substantially to gamma diversity in the NORI-D license area, with many fauna found only in the target mining zone and not in the respective preservation region. These results suggest that the designated preservation region of this license may not adequately represent a control site for monitoring impacts or safeguarding local biodiversity. We demonstrate the use of eDNA as a baseline surveying method at the scale of an exploration license area in this work. Chapter 3 quantifies temporal variability in the abyssal benthopelagic plankton and larval communities of NORI-D collected via in-situ plankton pumps from paired cruises (22 deployments, avg. 14 m3 seawater/pump). High community turnover and changes in abundance between sampling periods was observed, suggesting a distinct community exists in the BBL under high and low organic matter flux events, with select taxa displaying seasonal reproductive cycles. These results suggest that biodiversity loss associated with polymetallic nodule mining is unlikely to be reduced if mining occurs only during select seasonal time periods, as high species richness and distinct community structure were observed in both sampling periods. Chapter 4 explores the influence of adult mobility and habitat requirement on abyssal biogeography among the benthic-boundary layer (BBL) zooplankton assemblage. Benthic, benthopelagic, and holoplanktonic assemblages were evaluated from collections across the eastern and western margins of the CCZ (four cruises, >3,700 km, 39 deployments). Community dissimilarity increased with increasing geographic distance across the abyssal seafloor, with increasing steepness in the relationship with increased affinity for the seafloor. Results suggest that increasing community dissimilarity with distance was not due to range limitation but rather a result of underlying habitat availability and habitat requirements. In Chapter 5, I describe the composition of the BBL plankton, with a focus on demersal larvae. Taxonomic data is presented for 48 morphotypes from 715 records using a combination of morphological and genetic approaches. This work represents the first morphotaxonomic and molecular faunal guide for the BBL zooplankton of the Pacific Ocean, and is an important step in facilitating adult-larval relationships in deep-sea ecology. This dissertation explores patterns of ecology across habitat, time, and space among abyssal invertebrates. A holistic methodological framework using molecular and morphotaxonomic techniques integrates information across size class, habitat, and life history. I demonstrate that abyssal communities of CCZ are highly diverse and dynamic, with biogeographic patterns influenced by dependency to the seafloor. A summary of the dissertation is found in Chapter 6, including a discussion of anthropogenic impacts and outstanding questions stimulated by this work.